This invention relates generally to a sensor, and more particularly to an improved construction for retaining a sensing element on a housing.
Japanese Laid-Open (Kokai) Patent Application Ser. No. 82918/85 and Japanese Laid-Open Utility Model Application Ser. No. 111662/87 disclose rotation sensors which are provided with one or more magnetic sensing elements, such as a Hall element and a magnetic resistance element, capable of sensing rotation of a very low speed. Such a conventional rotation sensor comprises a cylindrical housing, and the magnetic sensing element is mounted on the front end of the housing. The housing has at its outer peripheral surface external threads by which the housing is threadedly connected to a support member disposed in the vicinity of an objected to be sensed. A rotary disc is fixedly connected to the object to be sensed, the disc having a number of projections or alternate north and south magnetic poles on the peripheral surface of the rotary disc. The magnetic sensing element is disposed near the peripheral surface of the rotary disc, and outputs a pulse signal in accordance with the rotation of the rotary disc.
The magnetic sensing element is required to be accurately retained in position at the front end of the housing. Further, particularly where such a sensor is used for sensing either the rotation of an internal combustion engine or the rotation of a fuel supply device for such internal combustion engine, it is required that the front portion of the housing projecting from the support member should be reduced in diameter so as to occupy a less space. The rotation sensors of the above-mentioned Japanese applications do not meet these requirements satisfactorily. These conventional rotation sensors will now be described in detail.
With respect to the rotation sensor disclosed in the aforesaid Japanese Laid-Open Patent Application Ser. No. 82918/85, the housing has a greater-diameter portion, an elongate smaller-diameter portion, and a shoulder portion interconnecting the greater-diameter portion and the smaller-diameter portion, the smaller-diameter portion having an end wall at its distal end. The magnetic resistance elements (magnetic sensing elements), a magnet and a core are mounted within the smaller-diameter portion of the housing in this order from the distal end thereof, and are held against one another. The magnetic resistance elements are held against the end wall of the housing. A circuit board for waveform shaping purposes is mounted within the greater-diameter portion of the housing, the circuit board being disposed perpendicularly to the axis of the housing. The magnetic resistance elements are connected to this circuit board by lead wires. The magnetic resistance elements, the magnet and the core are retained in position by a resin filled in the housing. In this conventional rotation sensor, the front portion of the housing can be made narrow. However, since the magnetic resistance elements, the magnet and the core are retained only by the resin as described above, they can not be positively retained in position before the resin is filled in the housing. As a result, it is difficult to accurately mount the magnetic resistance elements in position.
With respect to the rotation sensor disclosed in the aforesaid Japanese Laid-Open Utility Model Application Ser. No. 111662/87, an elastic holder of a cylindrical shape is received in the front portion of the housing, and a circuit board for waveform shaping purposes is mounted within the proximal portion of the housing. The holder has a plurality of holes extending therethrough in parallel relation to the axis of the housing. A metal pipe is press-fitted into each of these holes. A cover is attached to the front end of the housing, and the Hall element (magnetic sensing element) is inserted in a hole formed through a central portion of the cover. A plurality of terminal wires of the Hall element pass respectively through the metal pipes, and are connected to the circuit board. Each of the terminal wires is soldered to the front end of a respective one of the metal pipes intermediate the opposite ends of the terminal wire. In this conventional rotation sensor, since the plurality of metal pipes are passed through the elastic holder, the diameter of the holder can not be reduced, and therefore the diameter of the front portion of the housing can not be reduced. Further, a plurality of component parts are needed for retaining the Hall element, and increased time and labor are required for the assemblage. This is disadvantageous in that increased costs are incurred.